[github] Remove commit hash from CP issue template (#139676)

* This seems to be unnecessary as users will open a CP PR with the original commit linked in it.
* Add note on changelog description to be less than 80 chars

.github/ISSUE_TEMPLATE/7_cherry_pick.yml

@@ -10,13 +10,6 @@ body:
       description: What is the link to the issue this cherry-pick is addressing?
     validations:
       required: true
-  - type: input
-    id: commit_hash
-    attributes:
-      label: Commit Hash
-      description: What is the shortened commit hash that has been merged to master/main?
-    validations:
-      required: true
   - type: dropdown
     id: Target
     attributes:
@@ -41,7 +34,7 @@ body:
     attributes:
       label: Changelog Description
       description: >-
-        Explain this CP in one line that is accessible to most Flutter developers
+        Explain this CP in less than 80 characters that is accessible to most Flutter developers
         See https://github.com/flutter/flutter/wiki/Hotfix-Documentation-Best-Practices for examples
     validations:
       required: true